Marker arms are used for forming marker furrows. The marker-arm mechanism includes an elongated marker arm and a marker disc, attached to the marker arm, for forming the marker furrow. A first end portion of the marker arm is mounted on a wheeled farm implement. The opposite end portion of the marker arm has the disc affixed thereto.
A tractor is used to pull the wheeled farm implement through the field. The marker arm mechanism includes means for causing the disc to penetrate the soil; and the marker arm, being moved over the ground by the tractor, causes the soil-penetrating disc to be dragged across the soil in a soil-penetrating manner, thereby forming a linear "marker" furrow. For the marker arm, this is referred to as the "working position."
Wheeled farm implements, in addition to carrying one or two marker-arm mechanisms, generally also carry a plurality of ground-tool implements. For example, one conventional ground-tool implement is a so-called "row unit" which includes a disc and a press-wheel assembly. The row-unit disc opens a furrow in the soil, another device on the farm implement deposits seeds at appropriate spaced intervals in the row-unit furrow, and the press wheel loosely covers the seeds with moist soil. Conventional tractors pull wheeled farm implements having 42-56 row units attached. Row planters of this sort are thus used to form a plurality of parallel-spaced seed-implanted furrows as the tractor operator makes a pass through the field. Accordingly, a single pass of seed-implanted furrows of a row planter can be quite wide.
The object of using a marker arm, to form a marker furrow, is to space consecutive passes as close to each other as possible without overlap and without permitting unworked areas of the field to form between furrows formed by successive passes of the row units through the field. Overlap, for example, tends to waste seed, which can be costly to the farmer; and unworked areas reduce the farmer's yield-to-acre ratios, which is similarly undesirable. After completing a pass and turning his tractor around to form a subsequent pass, a tractor operator will generally center his tractor on the just-formed marker furrow, to guide him as he forms the subsequent pass.
Conventional markers are somewhat fragile, being perhaps 3 to 4 inches across in transverse cross section and 20 to 25 feet in length. Because of length considerations, most commercial marker arms are constructed of pivoted, bifolded members. Until use is required, the conventional marker arm is typically folded and disposed generally vertically relative to the ground. This is referred to as the "transport position" for the marker arm.
It is desirable that a marker disc be able to follow most ground contours, when the field is not level, so as to provide the tractor operator with a somewhat continuous marker furrow for lining up his tractor on his next pass. The problem with the way most conventional marker arms are mounted to wheeled implements, however, is that little or no design consideration is given to freedom of movement of the marker arm, independent of the surface-following movement of the farm implement. That is, the disposition of conventional marker arms toward the ground, because the marker arms are mounted onto the wheeled implement, is governed to a major extent by the way the wheeled implement follows the ground contours. However, for reasons discussed above, the marker disc is spaced a considerable distance from the wheeled implement; and, as a result, ground contours influencing attitude of the wheeled implement relative to the horizontal may be quite different, in elevation or depression, from the ground contours to which the marker disc is being exposed. One disadvantage of such marker arm design is that significant damage can be caused when marker arm movement becomes restrained by a hill or when a marker arm is snagged by rocks, trees, fence posts or other obstacles during field and transport operation. It is desirable, therefore, to permit the marker disc to follow ground contours, substantially independent of the influence of the wheeled farm implement.
Movement of the marker arm from the transport to the field position is typically caused by a hydraulic cylinder mechanism powered by the tractor. Such conventional hydraulic mechanisms typically include double-acting hydraulic cylinders which require two pairs of hydraulic fluid lines. That is, a first set of hydraulic fluid lines is required to actuate the hydraulic cylinder piston rod to extend or retract to dispose the marker arm outwardly into the field position; and a second set of hydraulic lines is required to return the marker arm to the transport position. Typically, the tractor generates the power required to pump hydraulic fluid, which actuates the double-acting hydraulic cylinder, for extending and retracting the marker arm. It is desirable to make more efficient use of tractor power during raising and lowering of the marker arm.